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Nematode Uptake Preference toward Different Nanoplastics through Avoidance Behavior Regulation
Summary
Scientists discovered that tiny roundworms actively avoid certain nanoplastics based on their size and surface charge, with more toxic particles triggering stronger avoidance behavior through the insulin signaling pathway. Smaller (100 nm) and positively charged nanoplastics provoked the strongest defense response, leading to lower accumulation in the worms. Since this avoidance pathway is genetically similar across many species, the findings suggest that organisms throughout the food chain may preferentially ingest certain types of nanoplastics over others, affecting how these particles move through ecosystems toward humans.
Expounding bioaccumulation pathways of nanoplastics in organisms is a prerequisite for assessing their ecological risks in the context of global plastic pollution. Invertebrate uptake preference toward nanoplastics is a key initial step of nanoplastic food chain transport that controls their global biosafety, while the biological regulatory mechanism remains unclear. Here, we reveal a preferential uptake mechanism involving active avoidance of nanoplastics by <i>Caenorhabditis elegans</i> and demonstrate the relationship between the uptake preference and nanoplastic characteristics. Nanoplastics with 100 nm in size or positive surface charges induce stronger avoidance due to higher toxicity, causing lower accumulation in nematodes, compared to the 500 nm-sized or negatively charged nanoplastics, respectively. Further evidence showed that nematodes did not actively ingest any types of nanoplastics, while different nanoplastics induced defense responses in a toxicity-dependent manner and distinctly stimulated the avoidance behavior of nematodes (ranged from 15.8 to 68.7%). Transcriptomics and validations using mutants confirmed that the insulin/IGF signaling (IIS) pathway is essential for the selective avoidance of nanoplastics. Specifically, the activation of DAF-16 promoted the IIS pathway-mediated defense against nanoplastics and stimulated the avoidance behavior, increasing the survival chances of nematodes. Considering the genetical universality of this defense response among invertebrates, such an uptake preference toward certain nanoplastics could lead to cascaded risks in the ecosystem.
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